Describe differences to directly working with the File System Access API in README

[thien-do]

Hi :D If you're ok, I'd like to have a small PR to add a small section to the README regarding the migration from the native file system.

Thing is, I used the native file system first, then as my app needs to go live, I adopt this library, and there are several things I learned that I think would be useful for others in similar situation.

For example:

• In the native API, the main model is "handle", and you get the file content from there, async
• In this API, the main model is the file itself, and the "handle" is an optional object
• Stuff like persisting to local storage (indexed DB actually)

[tomayac]

I like this idea. I would just call it "differences" rather than "migrating". The differences are that we need to be compatible with the legacy approach from an API input/output point of view. Please go ahead, and thanks again!

[tomayac]

If you're ok, I'd like to have a small PR to add a small section to the README regarding the migration from the native file system.

@thien-do Friendly ping, are you still interested in this?

[thien-do]

Hey @tomayac , sorry I can't do it :(